Correlation of Electron-Transfer Rates with the Surface Density of States of Native and Anodically Grown Oxide Films on Titanium.

摘要

We report tunneling spectroscopy (TS) and surface density of states (SDOS) plots ((dI/dV)/(IV) vs V) for native and anodically grown titanium dioxide (TiO2) film on polycrystalline Ti. The results are compared to data obtained using single crystal TiO2 ((001 and (110) surface orientations). SDOS plots for anodically grown TiO2 films (160A thick) and single crystal TiO show a large band-gap region (approx. 2eV) with a low state density separating the conduction and valence band edges. The similarity in the distribution of SDOS for anodically grown film has a well-ordered rutile structure. In contrast, SDOS plots obtained on native TiO2 films show a nearly constant density of states over a 5 eV range and a approx. 25-fold increase in state density at energies corresponding to the band-gap region of anodically grown films and single crystal TiO2. Electron transfer rates for the oxidation of ferrocene in acetonitrile at native and anodically grown TiO2 films are reported and correlated with the measured SDOS of these materials.